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Maximum GPM and supply line

I have a 5/8 inch water meter next to the street near the city water main. I have a 3/4 inch copper pipe coming into the water meter and a 3/4 inch pipe going to the house. So technically my service line is 3/4 inch. I plan to tap in for my irrigation system right at the water meter with a 1 inch main line going to irrigtation system. I have read I can use 15 GPM as my max GPM instead of 10 GPM because I am tapping in right near the water meter and is so close to the water main. Is this correct? I just want to make sure because the difference is huge. TIA for any info you give.

PS My static pressure is 80 PSI just in case you need that information.

I'm not exactly sure how psi relates to gpm.
Yes the best place to hook on is closer to the meter. You don't lose some of your flow do to the length of the 3/4' main water line.
You need to have at least 40 psi throughout your sprinkler system to get good pressure through the heads. I don't know if you have ever heard of the bucket test to find out gpm. but it works like this: After hooking into your main water line, it may be easier to just have someone with the equipment do it. But this is what you would need: A gadget with a water flow control followed by a pressure gauge, a 5 gallon bucket and a watch. hook onto your line that you connected to the main water line. It's usually best to put the main sprinkler valve on then hook on to it. Anyways with your gadget. Close off the water until the gauge reads 40 psi. All the water coming out of gadget at that point is free to use for your system. Take a 5 gallon bucket and time how long it takes to fill it. 60 seconds / time to fill bucket times 5 gives you your gpm.